Scientific American Supplement, No. 324, March 18, 1882
by
Various
Part 1 out of 3
Produced by Olaf Voss, Don Kretz, Juliet Sutherland,
Charles Franks and the DP Team
[Illustration]
SCIENTIFIC AMERICAN SUPPLEMENT NO. 324
NEW YORK, MARCH 18, 1882
Scientific American Supplement. Vol. XIII, No. 324.
Scientific American established 1845
Scientific American Supplement, $5 a year.
Scientific American and Supplement, $7 a year.
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TABLE OF CONTENTS.
I. ENGINEERING AND MECHANICS--Machine Tools for Boiler Makers.
2 figures.--Improved boiler plate radial drill.--Improved
boiler plate bending roller.
Modern Ordnance. By COLONEL MAITLAND.--Rifled cannon.--Built
guns.--Steel castings.--Breech loading.--Long guns.--Slow
burning of powder.--Breech closers.--Projectiles.--Destructive
power of guns.
Oscillating Cylinder Locomotive. 2 figures.--Shaw's oscillating
cylinder locomotive.
Gas Motors and Producers. By C. W. SIEMENS--2 figures.
The Bazin System of Dredging. By A. A. LANGLEY.--3 figures.
II. CHEMISTRY.--On the Mydriatic Alkaloids. By ALBERT LADENBERG.
--I. Atropine.--II. The Atropine of Datura Stramonium.
--III. Hyoscyamine from Hyoscyamus.
Detection of Small Quantities of Morphia. By A. JORISSEN.
The Estimation of Manganese by Titration. By C. G. SARNSTROM.
On the Estimation and Separation of Manganese. By NELSON
H. DARTON.
Delicate Test for Oxygen.
Determination of Small Quantities of Arsenic in Sulphur. By H.
SCHAEPPI.
III. BIOLOGY, ETC.--Researches on Animals Containing Chlorophyl.
--Abstract of a long and valuable paper "On the Nature and Functions
of the Yellow Cells of Radiolarians and Coelenterates," read
to the Royal Society of Edinburgh. By PATRICK GEDDES.
The Hibernation of Animals, An interesting review of the winter
habits of some of our familiar animals, insects, etc.
IV. HORTICULTURE, SILK CULTURE, ETC.--How to Plant Trees.
By N. ROBERTSON.
The Growth of Palms.
The Future of Silk Culture in the United States. Report of
United States Consul Peixotto, of Lyons. A valuable and encouraging
summary of the conditions and prospects of silk culture
in the United States.
V. TECHNOLOGY, ETC.--Compressed Oil Gas for Lighting Cars,
Steamboats, and Buoys. An elaborate description of the apparatus
and appliances of the Pintsch system of illumination. 14
figures. Elevation and plan of works.--Cars.--Locomotive and car
lamps.--Buoys.--Regulations, etc.
VI. ART, ARCHITECTURE, ETC.--Cast Iron in Architecture.
VII. ELECTRICITY, MAGNETISM, ETC.--On the Mechanical Production
of Electric Currents. 12 figures.
Rousse's Secondary Battery.
VIII. MISCELLANEOUS.--Dangers from Lightning in Blasting.
The Tincal Trade of Asia.
Sir W. Palliser. Obituary and summary of his inventions.
The Tides. Influence of the tides upon the history of the earth.
Drilling Glass.
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MACHINE TOOLS FOR BOILER-MAKERS.
We give this week an engraving of a radial drilling machine designed
especially for the use of boiler-makers, this machine, together with the
plate bending rolls, forming portion of a plant constructed for Messrs.
Beesley and Sons, boiler makers, of Barrow-in-Furness.
[Illustration: IMPROVED BOILER PLATERADIAL DRILL.]
This radial drill, which is a tool of substantial proportions, is
adapted not only for ordinary drilling work, but also for turning the
ends of boiler shells, for cutting out of flue holes tube boring, etc.
As will be seen from our engraving, the pillar which supports the radial
arm is mounted on a massive baseplate, which also carries a circular
table 6 ft. in diameter, this table having a worm-wheel cast on it
as shown. This table is driven by a worm gearing into the wheel just
mentioned. On this table boiler ends up to 8 ft. in diameter can be
turned up, the turning tool being carried by a slide rest, which is
mounted on the main baseplate, as shown, and which is adjustable
vertically and radially.
For cutting out flue holes a steel boring head is employed, this head
having a round end which fits into the center of the table. When this
work is being done the radial arm is brought into the lowest position.
Flue holes 40 in. in diameter can thus be cut out.
The machine has a 4 in. steel spindle with self-acting variable feed
motion through a range of 10 in., and the radial arm is raised or
lowered by power through a range of 2 ft. 8 in. When the arm is in its
highest position there is room for a piece of work 4 ft. high between
the circular table and the lower end of the spindle. The circular
table serves as a compound table for ordinary work, and the machine is
altogether a very useful one for boiler-makers.
The plate-bending rolls, which are illustrated on first page, are 10 ft.
long, and are made of wrought iron, the top roll being 12 in. and the
two bottom rolls 10 in. in diameter. Each of the bottom rolls carries
at its end a large spur-wheel, these spur-wheels, which are on opposite
sides of the machine, each gearing into a pinion on a shaft which runs
from end to end below the rolls, and which is itself geared to the shaft
carrying the belt pulleys, as shown. This is a very simple and direct
mode of driving, and avoids the necessity for small wheels on the rolls.
There is no swing frame, but the top roll is arranged to draw through
between the arms of the spur-wheels, a very substantially framed machine
being thus obtained.
[Illustration: IMPROVED BOILER PLATE BENDING ROLLER.]
The chief novelty in the machine is the additional roll provided
under the ordinary bottom rolls. This extra roll, which is used for
straightening old plates and for bending small tubes, pipes, etc., is
made of steel, and is 7 in. in diameter by 5 ft. long. It is provided
with a swing frame at one end to allow of taking-off pipes when bent,
etc., and it is altogether a very useful addition.
The machine we illustrate weighs 11 tons, and is all self-contained, the
standards being mounted on a strong bedplate, which also carries the
bearings for the shaft with fast and loose pulleys, belt gear, etc. Thus
no foundation is required.--_Engineering_.
* * * * *
MODERN ORDNANCE.
[Footnote: A paper read Feb. 8, 1882, before the Society of Arts,
London.]
By COLONEL MAITLAND.
A great change has lately been taking place throughout Europe in the
matter of armaments. Artillery knowledge has been advancing "by leaps
and bounds;" and all the chief nations are vying with each other in the
perfection of their _materiel_ of war. As a readiness to fight is the
best insurance for peace, it behooves us to see from time to time how we
stand, and the present moment is a peculiarly suitable one for taking
stock of our powers and capabilities. I propose, therefore, to give you,
this evening, a brief sketch of the principles of manufacture of
modern guns, at home and abroad, concluding with a few words on their
employment and power.
The introduction of rifled cannon into practical use, about twenty years
ago, caused a complete revolution in the art of gun-making. Cast iron
and bronze were found no longer suitable for the purpose. Cast iron was
too brittle to sustain the pressure of the powder gas, when its duration
was increased by the use of elongated projectiles; while the softness of
bronze was ill adapted to retain the nicety of form required by accurate
rifling.
From among a cloud of proposals, experiments, and inventions, two
great systems at length disentangled themselves. They were the
English construction of built-up wrought iron coils, and the Prussian
construction of solid steel castings.
Wrought-iron, as you are all aware, is nearly pure iron, containing but
a trace of carbon. Steel, as used for guns, contains from 0.3 to 0.5 per
cent of carbon; the larger the quantity of carbon, the harder the steel.
Since the early days of which I am now speaking, great improvement has
taken place in the qualities of both materials, but more especially in
that of steel. Still the same general characteristics were to be noted,
and it may be broadly stated, that England chose confessedly the weaker
material, as being more under control, cheaper, and safer to intrust
with the lives of men; while Prussia selected the stronger but less
manageable substance, in the hope of improving its uniformity, and
rendering it thoroughly trustworthy. The difference in strength, when
both are sound, is great. Roughly, gun steel is about twice as strong as
wrought iron.
I must now say a few words on the nature of the strains to which a piece
of ordnance is subjected when fired. Gunpowder is commonly termed an
explosive, but this hardly represents its qualities accurately. With a
true explosive, such as gun-cotton, nitro glycerine and its compounds,
detonation and conversion of the whole into gas are practically
instantaneous, whatever the size of the mass; while, with gunpowder,
only the exterior of the grain or lump burns and gives off gas, so that
the larger the grain the slower the combustion. The products consist of
liquids and gases. The gas, when cooled down to ordinary temperature,
occupies about 280 times the volume of the powder. At the moment of
combustion, it is enormously expanded by heat, and its volume is
probably somewhat about 6,000 times that of the powder. I have here a
few specimens of the powders used for different sizes of guns, rising
from the fine grain of the mountain gun to the large prisms and
cylinders fired in our heavy ordnance. You will readily perceive that,
with the fine-grained powders, the rapid combustion turned the whole
charge into gas before the projectile could move far away from its seat,
setting up a high pressure which acted violently on both gun and shot,
so that a short, sharp strain, approximating to a blow, had to be
guarded against.
With the large slow-bursting powders now used, long heavy shells move
quietly off under the impulse of a gradual evolution of gas, the
presence of which continues to increase till the projectile has moved a
foot or more; then ensues a contest between the increasing volume of the
gas, tending to raise the pressure, and the growing space behind the
advancing shot, tending to relieve it. As artillery science progresses,
so does the duration of this contest extend further along the bore
of the gun toward the great desideratum, a low maximum pressure long
sustained.
When quick burning powder was used for ordnance, the pressures were
short and sharp; the metal in immediate proximity to the charge was
called upon to undergo severe strains, which had scarcely time to reach
the more distant portions of the gun at all; the exterior was not nearly
so much strained as the interior. In order to obviate this defect, and
to bring the exterior of the gun into play, the system of building up
guns of successive tubes was introduced. These tubes were put one over
the other in a state of tension produced by "shrinkage." This term is
applied to the process of expanding a tube by the application of heat,
and in that condition fitting it over a tube larger than the inner
diameter of the outer tube when cold. When the outer tube cools it
contracts on the inner tube and clutches it fast. The wrought-iron guns
of England have all been put together in this manner.
Prussia at first relied on the superior strength of solid castings
of steel to withstand the explosive strain, but at length found the
necessity for re-enforcing them with hoops of the same material, shrunk
on the body of the piece.
The grand principle of shrinkage enables the gunmaker to bring into play
the strength of the exterior of the gun, even with quick powders, and to
a still greater extent as the duration of the strain increases with the
progress of powder manufacture. Thus, taking our largest muzzle-loaders
designed a few years ago, the thin steel lining tube, which forms an
excellent surface, is compressed considerably by the wrought-iron breech
coil holding it, which, in its turn, is compressed by the massive
exterior coil. When the gun is fired, the strain is transmitted at once,
or nearly at once, to the breech coil, and thence more slowly to the
outer one. Now, as the duration of the pressure increases, owing to the
use of larger charges of slower burning powder, it is evident that the
more complete and effective will be the transmission of the strain to
the exterior, and, consequently, the further into the body of the
gun, starting from the bore, and traveling outward, does it become
advantageous to employ the stronger material. Hence, in England, we
had reason to congratulate ourselves on the certainty and cheapness
of manufacture of wrought iron coils, as long as moderate charges
of comparatively quick burning powder were employed, and as long as
adherence to a muzzle-loading system permitted the projectiles to move
away at an early period of the combustion of the charge. Then the
pressures, though sharp, were of short duration, and were not thoroughly
transmitted through the body of the gun, so that the solidity, mass,
and compression of the surrounding coils proved usually sufficient to
support the interior lining. Now that breech-loading and slow powders
have been introduced, these conditions have been changed. The strains,
though less severe, and less tending to explosive rupture, last longer,
and are more fully transmitted through the body of the gun. Sheer
strength of material now tells more, and signs have not been wanting
that coils of wrought iron afford insufficient support to the lining.
It becomes, therefore, advantageous to thicken the inner tube, and to
support it with a steel breech piece. Carrying this principle further,
we shall be led to substitute the stronger for the weaker metal
throughout the piece. This has been done by the Germans in the first
instance, and recently by the French also. It is probable that we shall
follow the same course. When I say "probable," I intentionally guard
myself against uttering a prediction. It is never safe to prophesy,
unless you know, as the American humorist puts it. And in this case we
do not know, for a very dangerous rival, once defeated, but now full of
renewed vigor, has entered the lists against forged steel as a material
for ordnance. This rival's name is _wire_. Tempered steel wires can
be made of extraordinary strength. A piece of round section, only one
thirty-fifth of an inch in diameter, will just sustain a heavy man.
If, now, a steel tube, suitable for the lining of a gun, be prepared by
having wire wound round it very tightly, layer over layer, it will be
compressed as the winding proceeds, and the tension of the wire will act
as shrinkage. You will readily understand that a gun can be thus formed,
having enormous strength to resist bursting. Unfortunately, the wires
have no cohesion with one another, and the great difficulty with
construction of this kind is to obtain what gun-makers call end
strength. It is of but little use to make your walls strong enough, if
the first round blows the breech out. In the early days of wire this was
what happened, and Mr. Longridge, who invented the system, was compelled
to abandon it.
Lately, methods have been devised in France, by M. Schultz; at Elswick,
by Sir W.G. Armstrong & Co.; and at Woolwich, by ourselves, for getting
end strength with wire guns. They are all in the experimental stage;
they may prove successful; but I prefer not to prophesy at present.
The diagrams on the wall show the general construction of the modern
German, French, and English heavy breech-loading guns. The Germans have
a tube, a jacket, and hoops. The French, a thick tube or body, and
hoops. The English, a tube, a jacket, and an overcoat, as it may be
called. In each system of construction, the whole of the wall of the gun
comes into play to resist the transverse bursting strain of the charge.
The longitudinal or end strength varies: thus, in the German guns, the
tube and hoops do nothing--the jacket is considered sufficient. The
French construction relies entirely on the thick body, while the English
method aims at utilizing the whole section of the gun, both ways.
Of course, if the others are strong enough, there is no particular
advantage in this; and it is by no means improbable that eventually we
shall find it cheaper, and equally good, to substitute hoops for the
"overcoat."
I fear I have detained you a long time over construction, but it is both
instructive and interesting to note that certain well defined points
of contact now exist between all the great systems. Thus, a surface of
steel inside the bore is common to all, and the general use of steel is
spreading fast. Shrinkage, again, is now everywhere employed, and
such differences as still exist are matters rather of detail than of
principle, as far as systems of construction are concerned.
We now come to a part of the question which has long been hotly debated
in this country, and about which an immense quantity of matter has been
both spoken and written on opposite sides--I mean muzzle loading and
breech-loading. The controversy has been a remarkable one, and, perhaps,
the most remarkable part of it has been the circumstance that while
there is now little doubt that the advocates of breech-loading were on
the right side, their reasons were for the most part fallacious. Thus,
they commonly stated that a gun loaded at the breech could be more
rapidly fired than one loaded at the muzzle. Now, this was certainly not
the case, at any rate, with the comparatively short guns which were
made on both systems a few years ago. The public were acquainted with
breech-loaders only in the form of sporting guns and rifles, and argued
from them. The muzzle-loading thirty eight ton guns were fired in a
casemate at Shoeburyness repeatedly in less than twenty minutes for ten
rounds, with careful aiming. No breech-loader of corresponding size has,
I think, ever beaten that rate. With field-guns in the open, the No. 1
of the detachment can aim his muzzle loader while it is being loaded,
while he must wait to do so till loading at the breech is completed.
Again, it was freely stated that, with breech-loaders greater protection
was afforded to the gunners than with the muzzle-loaders. This entirely
depends on how the guns are mounted. If in siege works or _en
barbette_, it is much easier to load a muzzle loader under cover than a
breech-loader. But I need not traverse the old ground all over again. It
is sufficient for me to say here, that the real cause which has rendered
breech-loading an absolute necessity is the improvement which has been
made in the powder. You witnessed a few minutes ago the change which
took place in the action of fired gunpowder when the grains were
enlarged. You will readily understand that nearly the whole of a quick
burning charge was converted into gas before the shot had time to start;
suppose for the moment that the combustion was really instantaneous.
Then we have a bore, say sixteen diameters long, with the cartridge
occupying a length of, say, two diameters.
The pressure of the gas causes the shot to move. The greater the
pressure, the greater the impulse given. As the shot advances, the
pressure lessens; and it lessens in proportion to the distance the shot
proceeds. Thus, when the shot has proceeded a distance equal to the
length of the cartridge, the space occupied by the gas is doubled, and
its original pressure is halved. As the shot travels another cartridge
length, the space occupied by the gas is trebled, and its pressure will
be but one-third of the original amount. When the shot arrives at the
muzzle--that is, at eight times the length of the cartridge from the
breech--the pressure will be but one ninth of that originally set up.
Remember, this is on the supposition that the powder has been entirely
converted into gas before the shot begins to move.
Now, suppose the powder to be of a slow-burning kind, and assume that
only one-third of it has been converted into gas before the shot starts,
then the remaining two-thirds will be giving off additional gas as the
shot travels through the bore. Instead, therefore, of the pressure
falling rapidly, as the shot approaches the muzzle, the increasing
quantity of gas tends to make up for the increasing space holding it.
You will at once perceive that the slower the combustion of the powder
the less difference there will be in the pressure exerted by the gas at
the breech and at the muzzle, and the greater will be the advantage,
in point of velocity, of lengthening the bore, and so keeping the shot
under the influence of the pressure. Hence, all recent improvement has
tended toward larger charges of slower burning powder, and increased
length of bore. And it is evident that the longer the bore of the gun,
the greater is the convenience of putting the charge in behind, instead
of having to ram it home from the front. I may here remark, that the
increased length of gun necessary to produce the best effect is causing
even those who have possessed breech-loaders for many years to rearm,
just as completely as we are now beginning to do. All the old short
breech loading guns are becoming obsolete. Another great advantage of
breech-loading is the facility afforded for enlarging the powder chamber
of the gun, so that a comparatively short, thick cartridge may be I
employed, without any definite restriction due to the size of the bore.
There is yet one more point in which breech-loading has recently been
found, in the Royal Gun Factory, to possess a great advantage over
muzzle-loading as regards ballistic effect. With a shot loaded from the
front, it is clear that it must be smaller all over than the bore, or it
would not pass down to its seat. A shot thrust in from behind, on the
contrary, may be furnished with a band or sheath of comparatively soft
metal larger than the bore; the gas then acting on the base of the
projectile, forces the band through the grooves, sealing the escape,
entering the projectile, and, to a great extent, mitigating the erosion
of surface. This is, of course, universally known. It is also pretty
generally known among artillerists that the effect of the resistance
offered by the band or sheathing on the powder is to cause more complete
combustion of the charge before the shot moves, and therefore to raise
the velocity and the pressure. But I believe it escaped notice, till
observed in May, 1880, in the Royal Gun Factory, that this circumstance
affords a most steady and convenient mode of regulating the consumption
of the charge, so as to obtain the best results with the powder
employed.
Supposing the projectile to start, as in a muzzle loader, without
offering any resistance beyond that due to inertia, it is necessary to
employ a powder which shall burn quickly enough to give off most of
its gas before the shot has proceeded far down the bore; otherwise the
velocity at the muzzle will be low. To control this comparatively quick
burning powder, a large air space is given to the cartridge, which,
therefore, is placed in a chamber considerably too big for it.
Supposing, on the other hand, the projectile to be furnished with a
stout band, giving a high resistance to initial motion, a much slower
powder can be used, since the combustion proceeds as if in a closed
vessel, until sufficient pressure is developed to overcome the
resistance of the band. This enables us to put a larger quantity of
slower burning powder into the chamber, and in fact to use, instead of a
space filled with air, a space filled with powder giving off gas, which
comes into play as the projectile travels down the bore. Thus, while not
exceeding the intended pressure at the breech, the pressure toward the
muzzle is kept up, and the velocity very materially increased. Following
this principle to this conclusion, it will be found that the perfect
charge for a gun will be one which exactly fills the chamber, and which
is composed of a powder rather too slow to give the pressure for which
the gun is designed, supposing the shot to move off freely. The powder
should be so much too slow as to require for its full development the
holding power of a band which is just strong enough to give rotation to
the shot.
Having settled that the gun of the future is to be a breech-loader,
we have next to consider what system of closing the breech is to be
adopted.
The German guns are provided with a round backed wedge, which is pushed
in from the side of the breech, and forced firmly home by a screw
provided with handles; the face of the wedge is fitted with an easily
removable flat plate, which abuts against a Broad well ring, let into
a recess in the end of the bore. On firing, the gas presses the ring
firmly against the flat plate, and renders escape impossible as long as
the surfaces remain uninjured. When they become worn, the ring and
plate can be exchanged in a few minutes. Mr. Vavasseur, of Southwark,
constructs his guns on a very similar plan. In the French guns, and our
modern ones, the bore is continued to the rear extremity of the piece,
the breech end forming an intermittent screw, that is, a screw having
the threads intermittently left and slotted away. The breech block has
a similarly cut screw on it, so that when the slots in the block
correspond with the untouched threads in the gun, the block can be
pushed straight in, and the threads made to engage by part of a
revolution. In the French Marine the escape of gas is stopped very much
as in Krupp's system; a Broadwell ring is let into a recess in the end
of the bore, and a plate on the face of the breech-block abuts against
it.
In the French land service the escape is sealed in quite a different
manner. A stalk passes through the breech-block, its foot being secured
on the exterior. The stalk has a mushroom-shaped head projecting into
the bore. Round the neck of the stalk, just under the mushroom, is a
collar of asbestos, secured in a canvas cover; when the gun is fired,
the gas presses the mushroom against the asbestos collar, and squeezes
it against the walls of the bore. It is found that this cuts off all
escape.
We are at present using the Elswick method, which consists of a
flat-backed cup, abutting against the slightly rounded face of the
breech plug. The lips of the cup rest against a copper ring let in the
walls of the bore. On firing, the gas presses back the cup against the
rounded end of the breech-block, and thus forces the lips hard against
the copper ring.
It is difficult to compare the excellence of these various systems, so
much depends on the care of the gunners, and the nicety of manufacture.
The German and French marine methods permit the parts to be quickly
exchanged when worn, but it is necessary to cut deeply into the walls
of the gun, and to make the wedge, or breech-screw, considerably larger
than the opening into the chamber.
The Elswick plan is decidedly better in this last respect, but it
requires several hours to extract and renew the copper ring where worn.
The French land service (_De Bange_) arrangement requires no cutting
into the gun, and no enlargement of the breech screw beyond the size of
the chamber, while it is renewable in a few minutes, merely requiring a
fresh asbestos pad when worn. As regards durability, there is probably
no great difference. I have been informed that with a light gun as many
as 3,000 rounds have been fired with one asbestos pad. But usually
it may be considered that a renewal will be required of the wearing
surfaces of any breech-loader after a number of rounds, varying from six
or seven hundred, with a field gun, to a hundred or a hundred and fifty
with a very heavy gun. Full information is wanting on this point.
Having now decided on the material of which the gun is to be composed,
and the manner in which it is to be constructed, and having, moreover,
settled the knotty point of how it is to be loaded, we come to the
general principles on which a gun is designed. It must not be overlooked
that a gun is a machine which has to perform a certain quantity of work
of a certain definite kind, and, like all other machines, must be formed
specially for its purpose. The motive power is gunpowder, and the
article to be produced is perhaps a hole in an armor-plate, perhaps a
breach in a concealed escarp, or perhaps destructive effect on troops.
These articles are quite distinct, and though all guns are capable of
producing them all to some extent, no gun is capable of producing more
than one in the highest state of excellence.
Thus, for armor piercing, a long pointed bolt, nearly solid, is
required. It must strike with great velocity, and must therefore be
propelled by a very large charge of powder. Hence an armor-piercing gun
should have a large chamber and a comparatively small bore of great
length.
For breaching fortifications, on the other hand, curved fire is
necessary; the escarps of modern fortresses are usually covered from
view by screens of earth or masonry in front, so that the projectiles
must pass over the crest of the screen, and drop sufficiently to strike
the wall about half-way down, that is to say, at an angle of 15 deg. to 20 deg..
To destroy the wall, shell containing large bursting charges of powder
are found to be particularly well adapted. Now it is clear that, for a
shell to drop at an angle of 15 deg. or 20 deg. at the end of a moderate range,
the velocity at starting must be low. Hence, for pieces intended for
breaching no enlarged powder chamber is wanted; the effect on the wall
is due to the shell, which must be made of a shape to hold the most
powder for a given weight; and, therefore, rather short and thick. This
gives us a large bore, which need not be long, as little velocity is
required.
For producing destructive effect among troops, a third kind of
projectile is employed. It is called shrapnel, and it consists of a thin
shell, holding a little powder and a large quantity of bullets. The
powder is ignited by a fuse, which is set to act during flight, or on
graze, when the shell is nearing the object. The explosion bursts the
shell open, and liberates the bullets, which fly forward, actuated by
the velocity of the shell at the moment of bursting. Hence, to render
the bullets effective, a considerable remaining velocity is requisite.
The gun must therefore take a large powder charge, while, as the shell
has to hold as many bullets as possible, the bore must be large enough
to take a short projectile of the given weight. Thus, the proportions
of the shrapnel gun will be intermediate between those of the
armor-piercing gun and the shell gun.
There are certain axioms known from experience, which should be
mentioned here. First, the length of the powder chamber should not
be more than three and a half or four times its diameter, if it can
possibly be avoided, because, with longer charges, the inflamed powder
gas is apt to acquire rapid motion, and to set up violent local
pressures. Next, the strength of a heavy gun, as reckoned on the
principle of all the metal being sound and well in bearing, should not
be less than about four times the strain expected.
Again, though there are several opinions as to the best weight of shot
for armor piercing, in proportion to diameter, yet among the most
advanced gun-makers, there is a growing tendency toward increased
weight. The value of w/d cubed, that is, the weight in pounds divided by the
cube of the diameter in inches, as this question is termed, is in the
hands of the Ordnance Committee, and it is to be confidently hoped that
efforts will shortly be made to arrive at a solution. In the meantime,
from about 0.45 to 0.5 appears to be a fairly satisfactory value, and is
adopted for the present.
Lastly, it may be broadly stated, that with suitable powders, a charge
of one-third the weight of the shot demands for most profitable use a
length of bore equal to about twenty-six calibers; a charge equal to
half the weight of the shot should be accommodated with a bore of about
thirty calibers; while a charge of two-thirds the weight of the shot
will be best suited by a bore thirty-five calibers long. Of course, in
each case, greater length of bore will give increased velocity, but it
will be gained at the expense of additional weight, which can be better
utilized elsewhere in the gun.
The amount of work performed by gunpowder, when exploded in a gun, is a
subject which has engaged a vast quantity of attention, and some highly
ingenious methods of calculating it have been put forward. Owing,
however, to the impossibility of ascertaining how fast the combustion
of large grains and prisms proceeds, a very considerable amount of
experience is required to enable the gunmaker to apply the necessary
corrections to these calculations; but, on the whole, it may be said
that, with a given charge and weight of shot, the muzzle velocity may
now be predicted with some accuracy.
You now have the chief data on which the designer bases his proposals,
and lays down the dimensions of the gun to suit such conditions as it
may be required to fulfill. In actual practice, the conditions are
almost always complicated, either by necessities of mounting in
particular places, such as turrets and casemates; or by the advantages
attending the interchangeability of stores, or other circumstances;
and it requires great watchfulness to keep abreast of the ever-growing
improvements of the day.
I will now conclude with a few words on the power of heavy guns, when
employed in various ways. The first consideration is accuracy of fire.
No matter how deadly the projectile may be, it is useless if it does
but waste itself on air. Accuracy is of two kinds--true direction and
precision of range. All modern guns are capable of being made to shoot
straight; but their precision of range depends partly on the successful
designing of the gun and ammunition, so as to give uniform velocities,
and partly on the flatness of the trajectory. The greater the velocity,
the lower the trajectory, and the greater the chance of striking the
target. Supposing a heavy gun to be mounted as in the fortresses round
our coasts, and aimed with due care, the distance of the object being
approximately known, we may fairly expect to strike a target of the size
of an ordinary door about every other shot, at a range of a mile and a
half. Here we have carriages mounted on accurately leveled platforms; we
have men working electric position finders, and the gunners live on the
spot, and know the look of the sea and land round about.
Now, consider the case of guns mounted in ships. You at once perceive
the difficulties of the shooter. Even supposing the ship to be one of
our magnificent ironclads, solid, steady, yielding little to the motion
of the water, yet she is under steam, the aim of her guns is altered
every moment, some oscillation is unavoidable, and she can only estimate
the range of her adversary. Great skill is required, and not only
required, I am glad to say, but ready to hand, on the part of the seamen
gunners; and low trajectory guns must be provided to aid their skill.
If we go to unarmored ships of great tonnage and speed, we shall
find these difficulties intensified; and if we pass on to the little
gunboats, advocated in some quarters for attacking ironclads in a swarm,
we shall find that unsteadiness of platform in a sea-way renders them a
helpless and harmless mark for the comparatively accurate practice of
their solitary but stately foe.
The destructive power of guns is little known to the general public, and
many wild statements are sometimes put forward. Guns and plates have
fought their battle with varying success for many years. One day the
plate resists, another day the gun drives its bolt through. But it is
frequently overlooked that the victory of a plate is a complete victory.
If the shot does not get through, it does practically nothing. On the
other hand, the victory of the gun is but a partial triumph; it is
confined to a small arc. I mean that, when the plate is struck at an
angle exceeding 30 deg. or so, the shot glances harmlessly off; while, even
when perforation is obtained, it is at the expense of the more deadly
qualities of the projectile, which must be a nearly solid bolt, unable
to carry in with it heavy bursting charges of powder or destructive
masses of balls.
About six years ago, an experiment carried out at Shoeburyness taught a
lesson which seems to be in danger of being forgotten. We hear sometimes
that unarmored vessels are a match for ironclads and forts; and I will
conclude this paper with a short extract from the official account of
the results of firing shrapnel shell at an unprotected ship's side. I
shall say nothing of boilers and magazines, but shall state simply the
damage to guns and gunners.
A target was built representing the side of a certain class of unarmored
ships of war; behind this target, as on a deck, were placed some
unserviceable guns, mounted on old carriages, and surrounded by wooden
dummies, to represent the men working the guns. The attacking gun was a
twelve-ton nine-inch muzzle-loader, of the old despised type, and the
projectiles were shrapnel shell. The charges were reduced to represent
the striking force at a range of 500 yards. Two rounds did the following
damage inside, besides tearing and ripping the ship's side in all
directions.
1st Gun.--Seven men of detachment killed.
2d Gun.--Carriage destroyed. Six men blown to pieces, all the remainder
of the detachment severely hit.
3d Gun.--No damage to gun or carriage. Five men killed, one blown to
bits, and one wounded in leg.
4th Gun.--Gun dismounted. The whole of the gun detachment blown to
pieces.
That is the amount of destruction achieved in an unarmored ship by two
rounds of shrapnel shell.
* * * * *
OSCILLATING CYLINDER LOCOMOTIVE.
This locomotive is the design of Mr. Henry F. Shaw, of Boston.
This engine has oscillating cylinders placed between the driving-wheels.
Fig. 2 represents a section of one of these cylinders, from which it
will be seen that each has two pistons and piston-rods, which are
connected directly to the crank-pins. His invention is described as
follows in his specification:
"Midway between each set of wheels, e and f, is located the oscillating
steam-cylinder, g, having its journals, g' and g", supported in the
stationary arm, h, which is secured in a suitable manner to the frame,
c. To each cylinder, g, is secured or cast in one piece therewith a
balanced vibratory beam or truss, i, as shown. Within the cylinder, g,
are two movable pistons, k and k', Fig. 2, provided with piston-rods, l
and l', and cross-heads, m and m', as shown.
"n n are slides for the cross-head, m, on the insides of one end of the
truss or beam, i, and n' n', are similar slides in the other end of
said truss or beam, for the cross-head, m'. To the driving-wheel, e,
is attached a crank-pin, passing through the cross-head, m, and to the
driver-wheel, f, is attached a similar crank-pin, F, that passes through
the cross-head, m'. o is the slide-valve within the steam-chest,
G, which slide-valve is operated forward and back by means of the
valve-rod, o, the outer end of which is hinged to the upper end of
the slotted lever, o squared, Fig. 1, that is hung at o cubed, on the end of the
balanced and vibratory beam of truss, i, as shown. On the crank, F, is
secured an eccentric, that works within the slot of the slotted lever,
o squared, during the revolution of the crank, F, and in this manner imparts
the requisite motion to the slide valve, o, to admit the steam into the
cylinder, g, alternately between the pistons, k and k', and at the ends
of said cylinder, g, so as to alternately force the pistons, k and k',
from and toward each other, and thus, in combination with the vibratory
motion of the truss, i, impart a rotary motion to the driving-wheels, e
and f.
[Illustration: SHAWS OSCILLATING CYLINDER LOCOMOTIVE.]
"The steam is admitted to and from the cylinder, g, as follows: When
the pistons, k and k', are at the outer ends of their stroke the steam
enters through the channel, p, back of the piston, k, and at the same
time through the channel, p', back of the piston, k', and thus causes
both pistons to move toward each other, the steam between them being
at the same time exhausted through the channels, q and q', the former
communicating with the exhaust, r, by means of the space, s, in the
valve, o, and the latter communicating with the exhaust, r', through the
channel, s', in the said valve, o. The steam that passes to the back of
the piston, k, comes direct from the steam-chest, G, through the open
end of the channel, p, the valve, o, being at this time moved to one
side to leave the port, p, open. The steam is admitted to the back end
of the piston, k', from the steam-chest, G, through the channel, s", in
the valve, o, and from thence to the channel, p'. When the pistons, k
and k', have reached their inner positions the live steam is admitted
through the channels, q and q', direct from the steam-chest, G, to the
former, and through the recess, s cubed, and channel, s', in the valve, o, to
the latter, the exhaust steam back of the piston, K, passing out through
the channel, p, to the recess, s, in the valve, o, and thence to the
exhaust, r, the exhaust steam back of the piston, k, passing out through
channel, p', and through channel, s", in the valve, o, and thence to the
exhaust, r'.
"The valve-rod, o', is to be connected to a link and reversing lever as
usual, such being, however, omitted in the drawings."
The advantages claimed for it are that "it is composed of very few
parts, and it is very powerful on account of its having a separate steam
actuating piston for each of its driving-wheels. It has great strength
and resistance, owing to the fact that no pressure is exerted on the
journals on which the steam cylinders oscillate, and all the pressure
from the steam pistons is directly transferred to the crank-pins on the
driving-wheels. The engine is perfectly balanced in any position during
the stroke, and it may therefore be run at a much higher speed than the
common engines now in use."
* * * * *
GAS MOTORS AND PRODUCERS.
By C.W. SIEMENS, London.
The cylinder of the engine--assuming that it has only a single-acting
one, placed with its axis vertical--consists of two parts; the upper hot
part being lined with plumbago, fire-clay, or other refractory material,
and the lower part kept cool by a water casing. The cylinder has a trunk
piston working in the lower part, and on its upper side a shield that
almost fills the hot part of the cylinder when the piston is at the
extreme of its upstroke. The trunk-rod of the piston passes through a
stuffing-box in the cylinder bottom, and is connected to a crank on the
engine-shaft; and this (unless multiple cylinders are employed) carries
a heavy fly-wheel. From the lower end of the cylinder there is a passage
which, by means of a rotating or reciprocating slide, is alternately
put in communication with inlets for gas and air (regulated by suitable
cocks or valves) and with a strong receptacle. As the piston, makes its
upstroke, air and gas are drawn into the annular space surrounding its
trunk, and the mixed air and gas are compressed by the downstroke of
the piston, and delivered into the receptacle, in which considerable
pressure is maintained. The receptacle is made of cylindrical form, with
a domed cover of thin sheet metal; so that in case of excessive internal
pressure it can operate as a safety-valve to save the body of the
receptacle from damage. From the upper end of the cylinder there is
a passage that, by means of a rotating or reciprocating slide, is
alternately put in communication with the receptacle and with a
discharge outlet. In this passage are fixed a number of wire gauze
screens or pieces of metal with interstices. These constitute a
regenerator of heat, and also prevent a communication of flame from the
cylinder to the receptacle. In the upper end of the cylinder or of the
piston shield are provided electrodes which give an electric spark, or
a platinum wire which is rendered incandescent by a current from an
inductor or other source of electricity to ignite the combustible charge
of the cylinder. After the engine has been for some time at work,
the heat at the upper part of the cylinder may suffice for effecting
ignition without provision of other means for this purpose.
In combining such an engine with means for generating the combustible
gas, a gas producer is employed. In this producer a current of heated
air is introduced into the heart of a body of kindled fuel, and
the gases produced--partly by distillation and partly by imperfect
combustion of the fuel--are conveyed to the gas inlet of the cylinder
or pump of the engine. As the gas in leaving the producer is hot, it is
caused to pass through regenerating apparatus, to which it delivers a
large portion of its heat before it reaches the engine, and the air
which supplies the producer is made to pass through this regenerating
apparatus so as to take up the heat abstracted from the gas.
In the accompanying engravings, Fig. 1 shows a front elevation (partly
in section) of a pair of engines constructed according to this
invention. The lower part, A, of each cylinder is cooled by water
circulating through its casing. The upper part, B, is lined with
refractory material, such as fire-clay. The trunk piston, C, is made
hollow, and formed with a shield covered by refractory material to
protect the packing of the piston and the surface of the lower part of
the cylinder from heat. The pistons of the two cylinders are connected
by rods, D, to opposite cranks on the shaft, E. This shaft, by means of
bevel gear, F, works a revolving cylindrical valve, G, situated in a
casing between the two cylinders. The lowest part of this casing is
supplied with combustible gas and with air, in proportions capable of
being regulated by stopcocks or valves. The highest part of the casing
communicates with a discharge-pipe; and the middle part of it with a
reservoir which can be cut off from communication by a stopcock, so that
the charge in the reservoir may be retained when the engine is stopped.
The middle space of the hollow valve, G, communicates, by a number of
holes, with the middle space of the slide casing. It also, by means of a
port at its lower part, communicates alternately with the annular spaces
of the two cylinders; this communication in each case being made when
the piston is performing the latter part of its downstroke. The interior
of the slide also, by means of a second port at its upper part,
communicates alternately with the tops of the two cylinders; this
communication being in each case made while the piston is performing the
first portion of its downstroke. During the upstroke of each piston the
slide, by means of another port, makes communication alternately to each
cylinder from the bottom of the slide casing, and by means of a fourth
port make communication alternately from each cylinder to the top of the
slide casing. In the passage connecting the top of the slide casing
to each cylinder is placed a regenerator, consisting of a number of
perforated metal plates or sheets of wire gauze.
[Illustration: SIEMENS' GAS PRODUCER AND GAS MOTOR. Fig 1.]
In order that gas of poor quality or gas diluted with a large proportion
of air may be utilized, an igniting arrangement is employed which
operates as follows: I is a vessel containing a supply of hydrocarbon
oil, preferably of volatile character. From this vessel pipes lead to
two cocks, one for each cylinder; these corks being caused to revolve in
time with the engine-shaft by a chain, M, communicating motion from a
wheel on the engine shaft to a chain-wheel of equal size on the spindle
of the two cocks. The plug of each cock has on its side a small hollow,
which during one part of its revolution presents itself under the
oil-pipe, and receives a charge of oil. During another part of its
revolution, which is timed to correspond with the flow of gaseous
mixture to the cylinder, the hollow of the plug presents itself to the
bend of a pipe leading from the top of the cylinder to a port opening
into the cylinder below the regenerator, in which port are situated
two wires of platinum. These wires are connected with the brushes of a
commutator, K, on the engine-shaft, which commutator is in electrical
connection with the poles of a battery, dynamo-electric machine, or
other source of electricity. Instead of two wires to produce a spark, a
single wire may be arranged to become incandescent at the proper time
for ignition.
The operation of the engine is as follows: Each piston as it ascends
draws into the annular space under it a supply of gas and air in
proportion regulated by the cocks or valves, and as it descends it
forces this charge into the interior of the revolving valve and its
casing, and into the reservoir which communicates therewith. When either
piston is at the top of its stroke, the revolving valve admits to the
upper part of the cylinder a supply of the gaseous mixture from the
reservoir and valve casing, and this passes through the generator. At
the same time a portion of the charge passes by the pipe, and becomes
enriched by admixture of the hydrocarbon oil delivered to it by the
cock. The enriched mixture, in passing the platinum wires, which at that
time give an electrical spark, is ignited, and ignites the charge that
is passing through the regenerator into the cylinder. The mixture thus
ignited expands, and acting on the full area of the piston propels it
downward, the under side of the piston being at that time subject to
pressure only on its annular area. When the piston has completed its
down-stroke the passage is opened to the discharge-pipe, and the
expanded products of combustion then pass from the cylinder through the
regenerator, and are discharged. In their passage they give out to the
regenerator a large portion of their heat, which the charge entering
the cylinder for the next stroke receives in passing through the
regenerator.
[Illustration: SIEMENS' GAS PRODUCER AND GAS MOTOR. Fig 2.]
Fig. 2 is a vertical section of a gas producer and scrubber, which, as
stated above, may be employed in combination with engines such as have
been described for supplying them with combustible gas. The producer
is a vessel lined with refractory material. At the top it has a supply
opening covered by a cap, U, having a flange dipping into a sand joint.
At the bottom it has an opening surrounded by inclined bars, V, which
rest upon a water-pipe perforated with small holes, by which water
issues to cool the bars and generate vapor. This vapor rises along
with a limited supply of air through the incandescent fuel above, and
combustible gas is produced, which collects in the annular space, and
is led thence by a pipe to the scrubber. The scrubber is a vessel
containing in its lower part water, W, supplied by a pipe, and having an
overflow. By means of a perforated deflecting plate the gas is caused
to bubble through the water, whereby it is cleansed and cooled, and it
passes by a pipe, X, to supply the engine. The upper end of the vertical
pipe of the scrubber is made open and covered by a cap sealed in water
while the producer is at work. In starting the producer this cap is
removed and a chimney pipe put in its place, so as to give a draught for
kindling the fuel in the producer. When the fuel is kindled the chimney
is removed and the cap substituted, whereupon the suction of the engine
continues the draught as required.
* * * * *
THE BAZIN SYSTEM OF DREDGING.
By MR. A.A. LANGLEY.
This paper, lately read before the Institution of Mechanical Engineers,
London, is a description of the construction and working of a dredger
on M. Bazin's system, as used by the author for the past three years in
dredging sand and other material in Lowestoft Harbor. The dredger is
represented in its general features on next page, Fig. 1. The total
length of the hull is 60 ft., with 20 ft. beam. In the after part of the
hold is placed a horizontal boiler, A, which supplies steam to a pair
of inverted vertical engines, B. These engines drive, through belts and
overhead pulleys, a centrifugal pump, C, which discharges into the open
trough, H. The suction pipe, D, of this pump passes through the side of
the dredger, and then forms an elbow bent downward at an angle of 45
deg. To this elbow is attached a flexible pipe, E, 12 in. in diameter
and 25 ft. long, made of India-rubber, with a coil of iron inside
to help it to keep its shape. At the lower end of this pipe is an
elbow-shaped copper nozzle which rests on the bottom, and is fitted with
a grating to prevent stones getting into the pump and stopping the work.
The flexible tube is supported by chains that pass over the head of a
derrick, F, mounted at the stern of the dredger, and then round the
barrel of a steam winch. By this means the depth of the nozzle is
altered, as required to suit the depth of water.
A man stands at the winch, and lifts or lowers the pipe as is required,
judging by the character of the discharge from the pump. If the liquid
discharged is very dark and thick the nozzle is too deep in the sand
or gravel; if of a light color the pipe must be lowered. The best
proportion of water to sand is 5 to 1. When loose sand is the only
material to be dealt with, it can be easily sucked up, even if the
nozzle is deeply buried; but at other times stones interfere with the
work, and the man in charge of the flexible tube has to be very careful
as to the depth to which the nozzle may be buried in the sand. The pump
is shown in Figs. 2 and 3. The fan is 2 ft. diameter, and has only two
blades, a larger number being less efficient. The faces of the blades,
where they come in contact with the sand, are covered with flaps of
India-rubber. Small doors are provided at the side of the pump for
cleaning it out, extracting stones, etc. The fan makes 350 revolutions
per minute, and at that speed is capable of raising 400 tons of sand,
gravel, and stones per hour, but the average in actual work may be taken
at 200 tons per hour. This is with a 10-horse power engine, and working
in a depth of water varying from 7 ft. to 25 ft. The great advantage of
this dredger is its capability of working in disturbed water, where the
frames of a bucket dredger would be injured by the rise and fall of the
vessel.
[Illustration: THE BRAZIN SYSTEMEM OF DREDGING.]
Thus at Lowestoft bucket dredgers are used inside the harbor, and the
Bazin dredger at the entrance, where there are sand and gravel, and
where the water is more disturbed. The dredger does not succeed very
well in soft silt, because, owing to its slow precipitation, it runs
over the sides of the hopper barges without settling. Nor does it do for
dredging solid clay. It gives, however, excellent results with sand and
gravel, and for this work is much superior to the bucket dredger. The
experience in working was then described, showing that a great many very
discouraging failures preceded successful working, about a year being
expended in getting good results.
COST OF WORKING.
The vessel or barge for carrying the machinery and pumps cost L600, and
the contract price of the machinery and pumps was L1,200. But before the
dredger was taken over by the company the alterations before enumerated
had cost about L300, bringing the total for barge and dredger up to
L2,100. In building a second dredger this might of course be greatly
reduced. The cost of repairs for one month's working has been only L5.
The contractor receives for labor alone 1-1/8d. per ton, being at the
rate of about 13/4d. for the dredging and 3/8d. for taking to sea--a lead
of two miles--all materials being supplied to him. The consumption of
coal is at the rate of about 1 ton for 1,000 tons of sand dredged. At
Lowestoft Harbor the total amount of dredging has been about 200,000
tons yearly, but this is now much reduced in consequence of the pier
extension recently constructed by the author, which now prevents the
sand and shingle from the sea blocking the mouth of the harbor. The
total cost of working has been 2.572d. per ton. which with 10 per cent
interest on capital, 0.240d., makes the total cost per ton 2.812d. The
repairs to steam tug, hopper, barges, and dredger have averaged about
2d. per ton.
Before the discussion on the paper commenced, Mr. Langley remarked that
attempts had been made to connect the engine direct to the pump of a
Bazin dredger, but this arrangement failed, and the belt acted as a
safety arrangement and prevented breakage by slipping when the pump was
choked in any way. A new lock was constructed near Lowestoft a short
time ago, and the dredger pump was used to empty it; when half empty the
men placed a net in front of the delivery pipe and caught a cartload of
fish, many of which where uninjured. In the discussion Mr. Wallick, who
had superintended the use of the dredger at Lowenstoft, gave some of his
experience there, and repeated the information and opinions given by Mr.
Langley in the paper.
Mr. Ball, London agent for M. Bazin, said that as devised by M. Bazin
the pump was placed below water level, so that the head of water outside
should be utilized; but he--Mr. Ball--now placed the pump considerably
above water level, as no specially formed craft was thus necessary. He
also described some of the steps by which he had arrived at the present
arrangements of the whole plant, and gave some particulars of its
working. Mr. Crampton asked some questions, in reply to which Mr. Ball
said the longest distance they had carried the material was 1,200 yards
in two relays--namely, a second pump on a floating barge with special
engine. The distance to which they could carry the material depended
upon its character. Fine sand would travel well; mud would not, bowlders
would not, though gravel would. To give the water a rotary motion he had
inserted a helical piece of angle iron, and so prevented deposition.
* * * * *
DANGER FROM LIGHTNING IN BLASTING.
Although the accident in the tunnel in process of construction at Union
Hill by the New York, Ontario, and Western Railroad Company, which took
place on Tuesday afternoon, was happily attended with no loss of life or
serious injuries to the men employed in the shaft, it reads a new lesson
as to the firing of charges of powder by electricity, and one that
should be carefully noted by railway and civil engineers, and even
by the torpedo service of the United States. The exact cause of the
explosion has scarcely been fully and accurately set forth by the
various reports of the affair.
It appears that the wires usually employed lo supply the electric lamps
in the excavation were used for the purpose of firing the charges, being
disconnected from the electric light system for the moment and connected
with the explosives. As a rule, six charges were fired together, those
of the afternoon relay of men being exploded at very regular hours--the
last usually at 5:45 P.M. There were only sixteen men in the shaft,
and the work of connecting the wires had commenced, when the flash of
lightning that occurred at 5:42 P.M., suddenly charged the conductors
and produced the explosion.
There were two flashes of lightning between the hours of 5 and 6 o'clock
Tuesday afternoon, the first taking place at 5:23, and the second
nineteen minutes later. The former, according to testimony elicited by
our reporter, simply caused a slight perturbation of the lights in the
tunnel, but did not extinguish them. Five minutes later the work of
disconnection and reconnection began, but only two of the six charges
were ready for the pressure of the button when the last flash
interrupted the proceedings. The fact that the time of the explosion
corresponded to the second with that of the aerial electrical discharge
furnishes indubitable evidence that the accident was not caused by any
carelessness on the part the electrician in charge, and exonerates
all parties from blame. At the same time it should be remembered by
engineers in of such work that atmospheric electricity cannot be
altogether disregarded in such cases, and that as a source of accident
it may at any time prove dangerous. The concurrence of circumstances on
Tuesday was particularly fortunate. In the first instance only two of
the six charges had been connected with the firing battery, and in the
second the rock in which the charges were inserted was so peculiarly
soft and porous as to deaden the force of the eight pounds of giant
powder thus prematurely set off. Had the cartridges been set in the
harder and more solid rock of the east heading, instead of the west, and
the explosion taken place there, probably not a man in the shaft would
have escaped destruction. The lesson to engineers is one of no less
importance than if the whole number of men had been killed, and should
lead to the exercise of great care and precaution at times when the air
is charged with electrical energy.--_New York Times_.
* * * * *
CAST IRON IN ARCHITECTURE.
Whatever may be the misgivings entertained by many engineers respecting
the future use of cast iron for structures of certain kinds, it is clear
that for architectural purposes this material is likely to be employed
to an extent hardly contemplated by many who have looked upon it with
disfavor. At the present moment many buildings may be seen in London, in
which cast iron has been introduced instead of stone for architectural
features, and the substitution of cast iron for facades in many
warehouses and commercial buildings seems to show that, notwithstanding
the prejudices of the English architect against the importation of the
iron architecture of our transatlantic brethren, there is a prospect of
its being largely employed for frontages in which ample lighting and
strength are needed. The extensive window space necessary in narrow city
thoroughfares, and the difficulty of employing brick in large masses,
such as pilasters and lintels, have chiefly led to the adoption of
material having less of the uncertain durability and strength of either
stone or terra-cotta in its favor. Architects would gladly resort to the
last-named material if it could be procured in sufficient size and mass
without the difficulties attendant upon shrinkage in the burning, and
the winding and unevenness of the lines thereby caused. They have also
an even more tractable material in concrete ready to their hand, if they
would seriously bring themselves to the task of stamping an expressive
art upon it, instead of going on designing concrete houses as if they
were stone ones. Cast iron has the advantage of being a tried material;
it is well adapted for structures not liable to sudden weights or
to vibration, and so it has come to be used for features of an
architectural kind, by a sort of tacit acknowledgment in its favor.
Those who are desirous of seeing examples of its employment in fronts
of warehouses will find instances in Queen Victoria Street, Southwark
Street, and Bridge Road, and Theobalds Road, where the whole or portions
of fronts have been constructed of cast iron. At some corner premises in
Southwark, the piers as well as the windows are formed of cast iron,
the former being made to assume the appearance of projecting pilasters.
There is nothing to which the most captious critic could object in the
treatment adopted here; the pilasters and other features have plain
moulded members, and there is no principle of design in cast work which
has been violated--the only question being the purely aesthetic one--is
it justifiable to copy features in cast iron which have generally been
constructed in stone or marble? The answer is obvious: Certainly not,
when those features suggest the mass and proportions or treatment
proper only for stone or marble; but when they do not so represent the
material, it is quite optional for the architect to build up his front
with castings, if by so doing he can obtain greater rigidity of bearing,
strength, and durability. He ought, of course, to vary the proportions
of his pilasters and horizontal lintels, and make them more in accord
with the material. It is the wholesale reproduction of the more costly
and ornamental features, such as we see in many buildings of New York
and Philadelphia, where whole fronts are manufactured of cast iron and
sheet-metal, which has shocked the minds of architects of culture and
sensitive feeling. Such imitations and cheap displays outrage the artist
by the attempt to produce in cast or rolled metal what properly belongs
to a stone front.
Bearing this distinction in mind, we are not presuming too much to
assert that architects have in cast iron, when properly employed under
certain restrictions, a material which might be turned to account in
narrow fronts where the use of brick or stone piers would encroach too
much upon the space for light. For warehouse fronts, we have evidence
for thinking that the employment of iron might be attended with
advantage, especially in combination with brickwork for the main
vertical piers. Plain classic mouldings, capitals and bases of the Doric
or Tuscan order, are well suited for cast-iron supports to lintels or
girders. In one attempt to make use of the structural features of the
latter, the fronts of the girders between the piers are divided into
panels, the flanges and stiffening pieces to the webs forming an
effective framework for cast or applied ornament to be introduced. The
iron framework thus constructed lends itself to the minor divisions of
the window openings, which can be of wood. In the new Leaden Hall and
Metropolitan Fruit and Vegetable Markets, cast-iron fronts have
been largely employed, consisting of stanchions cast in the form of
pilasters, with horizontal connections and other architectural members.
Regarding the more constructive aspects of cast iron, the employment of
it in fronts having numerous points of support and small bearings is
clearly within the capabilities of the material. So long as it is used
in positions in which its resistance to compression is the chief office
it has to fulfill, cast iron is in its right place. In the fronts of
buildings, therefore, where it is made to carry the floors and rolled
joists, and the lintels of openings, either as piers, pilasters, or
simply as mullions of windows, it is strictly within its legitimate
functions. So with regard to lintels and heads of openings where short
spans exist, cast iron is free from the objection that can be urged
against it for long girders. In fact, no position is better fitted for a
brittle, granular material than that of a vertical framework to receive
windows and ornamentation, and for such purposes cast iron is, to our
minds, admirably suited.
For bridge-building the value of this metal has lately been much
disputed, though we have several notable examples of its use in the
earlier days for such structures. In fact, the use of cast iron for
structural purposes is not older than the time of Smeaton, who in 1755
employed it for mill construction, and about the same time the great
Coalbrookdale Viaduct was erected across the Severn near Broseley, which
gave an impetus to the use of cast iron for bridge construction. The
viaduct had a span of 100 feet, and was composed of ribs cast in two
pieces; it was erected from castings designed by Mr. Pritchard, of
Shrewsbury, an architect, and this circumstance is worthy of note as
showing that an architect really was the first to employ this material
for important structural work, and that the same profession was the
first to reject it upon traditional grounds. It is quite certain,
however, the bridge-builder lost no time in trying his hand upon so
tractable a material; for not long after Telford erected a bridge at
Buildwas of even a greater span, and the famous cast-iron bridge over
the river Wear at Sunderland was erected from the designs of Thomas
Paine, the author of the "Age of Reason." Iron bridges quickly followed
upon these early experiments, for we hear of several being built on
the arched system, and large cotton-mills being erected upon fireproof
principles at the commencement of the present century, the iron girders
and columns of one mill being designed by Boulton and Watt. A little
later, Eaton Hodgkinson proved by experiments the uncertainty of cast
iron with regard to tensile strength, which he showed to be much less
than had been stated by Tredgold. Cast iron was afterwards largely
adopted by engineers. The experiments of Hodgkinson supplied a safe
foundation of facts to work upon, and cast iron has ever since retained
its hold. Thomas Paine's celebrated bridge at Sunderland had a span of
236 feet and a rise of 34 feet, and was constructed of six ribs, and is
remarkable from the fact that the arched girder principle used in the
Coalbrookdale and Buildwas bridges was rejected, that the ribs were
composed of segments or voussoirs, each made up of 125 parts, thus
treating the material in the manner of stone. Each voussoir was a
cast-iron framed piece two feet long and five feet in depth, and these
were bolted together. The Southwark bridge over the Thames, by Sir
John Rennie, followed, in which a similar principle of construction is
adopted. There is much to be said in favor of a system which puts each
rib under compression in the manner of a stone arch, and which builds up
a rib from a number of small pieces. At least, it is a system based on
the legitimate use of cast iron for constructive purposes. The large
segmental castings used in the Pimlico bridge, and the new bridge
over the Trent at Nottingham, from Mr. M. O. Tarbotton's design, are
excellent examples of the arched girder system. The Nottingham bridge
has each rib made up of three I-shaped segments bolted together and
united transversely; the span is 100 feet in each of the three openings,
and the ribs are three feet deep at the springing, diminishing about six
inches at the crown. We have yet to learn why engineers have abandoned
the arched bridge for the wrought iron girder system, except that the
latter is considered more economical, and better fitted for bearing
tensile stress. Cast-iron bridges constructed as rigid arches, subject
to compression and composed of small parts, have all the mechanical
advantages of stone without some of its drawbacks, while artistically
they can be made satisfactory erections.--_Building News_.
* * * * *
SIR W. PALLISER.
We announce with regret the death of Major Sir William Palliser, which
took place suddenly on February 4, 1882. Sir William had been suffering
from disease of the heart for a considerable period, but we believe that
no one anticipated that the end was so near. For some twenty years Sir
William had devoted himself to the improvement of guns, projectiles,
and armor. To him is attributed the invention of the chilled-headed
projectiles which are known by his name. There seems to be no doubt that
chilled projectiles were suggested at Woolwich Arsenal, and even made,
before Sir William took the matter up, but there is excellent reason to
believe that Sir William knew nothing of this, and that the invention
was original with him; at all events, he, aided by the efforts of the
foundry and the laboratory at Woolwich, brought these projectiles to
perfection, and unless steel-faced armor defeat them they cannot be
said to have as yet met their match. A most valuable invention of the
deceased officer was the cut-down screw bolt for securing armor plates
to ships and ports. It was at one time feared that no fastening could be
got for armor plates, as on the impact of a shot the heads or the nuts
always flew off the bolts. The fracture usually took place just at the
point where the screw-thread terminated. Sir William adopted the bold
course of actually weakening the bolt in the middle of its length by
turning it down, so that the screw stands raised up instead of being cut
into the bolt, and by this simple device he changed the whole face of
affairs, and the expedient applied in other ways, such as by drilling
holes longitudinally down bolts, has since been extensively adopted
where great immunity from fracture is required.
It is, however, for the well-known converted gun that Sir William
Palliser's name will be best remembered. When our smooth-bore cast iron
guns became obsolete they were converted into the rifled compound guns
by a process which led to their being known as Palliser guns. The plan
was to bore out a cast iron gun and then to insert a wrought iron rifled
barrel consisting of two tubes of coiled iron one inside the other.
By the firing of a proof charge the wrought iron barrel was tightened
inside the cast iron casing. By this means we obtained a converted gun
at one-third of the cost of a new gun, and saved L140 on a 64-pounder
and L210 on an 80-pounder. The process of conversion involved no change
in the external shape of the gun, and it could, therefore, be replaced
upon the carriage and platform to which it formerly belonged. The
converted guns were placed upon wooden frigates and corvettes and upon
the land fronts of fortifications, and were adopted for the defense of
harbors. The many services Sir William Palliser had rendered to the
science of artillery secured him the Companionship of the Bath in 1868,
and knighthood in 1873. In 1874 he received a formal acknowledgment from
the Lords of the Admiralty of the efficiency of his armor bolts for
ironclad ships. His guns have been largely made in America and elsewhere
abroad; and in 1875 he received from the King of Italy the Cross of
Commander of the Crown of Italy. The youngest son of Lieutenant Colonel
Wray Palliser--Waterford Militia--he was born in Dublin in 1830, and was
therefore only fifty-two years of age. He was educated successively at
Rugby, at Trinity College, Dublin, and at Trinity Hall, Cambridge, and,
finally passing through the Staff College at Sandhurst, he entered the
Rifle Brigade in 1855, and was transferred to the Eighteenth Hussars in
1858. He remained in the service to the end of 1871, when he retired by
the sale of his commission. At the general election of 1880, Sir William
Palliser was returned as a Conservative at the head of the poll for
Taunton. In the House of Commons Sir William gave his chief attention
to the scientific matters on which his authority was so generally
recognized. Under the many disappointments and "unkind cuts," which
fall to the lot of the most successful inventors, Sir William Palliser
displayed qualities that won hearty admiration. The confidence with
which he left his last well-known experiment to be carried out in his
own absence almost under the directions of those whose professional
opinions were adverse to his own, may be called chivalrous. His
liberality and kindness of Colonel of the second Middlesex Artillery
Volunteers had gained him the affection of the entire corps; in short,
where it might naturally be expected that he should win respect, he won
the love of those who were thrown with him.--_The Engineer_.
* * * * *
THE CEDARS OF LEBANON.--Regulations were lately issued by Rustem Pasha
for the guidance of travelers and others visiting the Cedars of Lebanon.
These venerable trees have now been fenced in, but, with certain
restrictions, they will continue to be accessible to all who wish to
inspect them. In future no encampments will be permitted within the
enclosure, except in the part marked out for that purpose by the keeper,
nor may any cooking or camp fires be lighted near the trees.
* * * * *
ON THE MECHANICAL PRODUCTION OF ELECTRIC CURRENTS.
The object of these articles is to lay down in the simplest and most
intelligible way the principles which are concerned in the mechanical
production of electric currents. Every one knows now that electric
lights are produced from powerful currents of electricity generated in
a machine containing magnets and coils of wire, and driven by a steam
engine, or gas engine, or water-wheel. But of the thousands who have
heard that a steam engine can thus provide us with electric currents,
how many are there who comprehend the action of the generator or
dynamo-electric machine? How many, of engineers even, can explain where
the electricity comes from, or how the mechanical power is converted
into electrical energy, or what the magnetism of the iron magnets has
to do with it all? Take any one of the dynamo-electric machines of
the present date--the Siemens, the Gramme, the Brush, or the Edison
machine--of each of these there exist descriptions excellent in their
way, and sufficient for men already versed in the technicalities of
electric science. But to those who have not served an apprenticeship to
the technicalities--to all but professed electricians--the action
of these machines is almost an unknown mystery. As, however, an
understanding of the how and the why of the dynamo-electric machine or
generator is the very A B C of electrical engineering, an exposition
of the fundamental principles of the mechanical production of electric
currents demands an important place in the current science of the day.
It will be our endeavor to expound these principles in the plainest
terms, while at the same time sacrificing nothing in point of scientific
accuracy or of essential detail.
The modern dynamo-electric machine or generator may be regarded as
a combination of iron bars and copper wires, certain parts of the
machinery being fixed, while other parts are driven round by the
application of mechanical forces. How the movement of copper wires and
iron bars in this peculiar arrangement can generate electric currents is
the point which we are proposing to make clear. Friction has nothing
to do with the matter. The old-fashioned spark-producing "electrical
machine" of our youthful days, in which a glass cylinder or disk was
rotated by a handle while a rubber of silk pressed against it, has
nothing in common with the dynamo-electric generator, except that in
both something turns upon an axis as a grindstone or the barrel of
a barrel-organ may do. In the modern "dynamo" we cannot help having
friction at the bearings and contact pieces, it is true, but there
should be no other friction. The moving coils of wire or "armatures"
should rotate freely without touching the iron pole-pieces of the fixed
portion of the machine. In fact friction would be fatal to the action of
the "dynamo." How then does it act? We will proceed to explain without
further delay. There are, however, three fundamental principles to be
borne in mind if we would follow the explanation clearly from step to
step, and these three principles must be laid down at the very outset.
1. The first principle is that the existence of the energy of electric
currents, and also the energy of magnetic attractions, must be sought
for not so much _in the wire_ that carries the current, or _in the bar_
of steel or iron that we call a magnet, as _in the space that surrounds_
the wire or the bar.
2. The second fundamental principle is that the electric current is, in
one sense, quite as much a _magnetic_ fact as an electrical fact; and
that the wire which carries a current through it has magnetic properties
(so long as the current flows) and can attract bits of iron to itself as
a steel magnet does.
3. The third principle to be borne in mind is that to do work of any
kind, whether mechanical or electrical, requires the expenditure of
energy to a certain amount. The steam engine cannot work without its
coal, nor the laborer without his food; nor will a flame go on burning
without its fuel of some kind or other. Neither can an electric current
go on flowing, nor an electric light keep on shedding forth its beams,
without a constant supply of energy from some source or other.
[Illustration: Fig. 1.]
The last of these three principles, involving the relation of electric
currents to the work they can do and to the energy expended in their
production, will be treated of separately and later. Meantime we resume
the task of showing how such currents can be produced mechanically, and
how magnetism comes in in the process.
[Illustration: Fig. 2]
Surrounding every magnet there is a "field" or region in which the
magnetic forces act. Any small magnet, such for example as a compass
needle, when brought into this field of force, exhibits a tendency to
set itself in a certain direction. It turns so as to point with its
north pole toward the south pole of the magnet, and with its south pole
toward the north pole of the magnet; or if it cannot do both these
things at once, it takes up an intermediate position under the joint
action of the separate forces and sets in along a certain line. Such
lines of force run through the magnetic "field" from one pole of the
magnet to the other in curves. If we define a line of force as being the
line along which a free north-seeking magnetic pole would be urged, then
these lines will run from the north pole of the magnet round to the
south pole, and pass through the substance of the magnet itself. In Fig.
1 a rough sketch is given of the lines of magnetic force as they emerge
from the poles of a bar magnet in tufts. The arrow heads show the
direction in which a free north pole would move. These lines of forces
are no fiction of the imagination, like the lines of latitude and
longitude on the globe; they exist and can be rendered visible by the
simplest of expedients. When iron filings are sprinkled upon a card or
a sheet of glass below which a magnet is placed, the filings set
themselves--especially if aided by a gentle tap--along the lines of
force. Fig. 2 is a reproduction from nature of this very experiment, and
surpasses any attempt to draw the lines of force artificially. It
is impossible to magnetize a magnet without also in this fashion
magnetizing the space surrounding the magnet; and the space thus filled
with the lines of force possesses properties which ordinary unmagnetic
space does not possess. These lines give us definite information about
the magnetic condition of the space where they are. Their direction
shows us the direction of the magnetic forces, and their density shows
us the strength of the magnetic forces; for where the force is strongest
there we have the lines of force most numerous and most strongly
delineated in the scattered filings. To complete this first
consideration of the magnetic field surrounding a magnet, we will take a
look at Fig. 3, which reproduces the lines of filings as they settle in
the field of force opposite the end of a bar magnet. The repulsion of
the north pole of the magnet upon the north poles of other magnets would
be, of course, in lines diverging radially from the magnet pole.
[Illustration: Fig. 3]
We will next consider the space surrounding a wire through which a
current of electricity is flowing. This wire has magnetic properties so
long as the current continues, and will, like a magnet, act on a compass
needle. But the needle never tries to point toward the wire; its
tendency is always to set itself broadside to the current and at right
angles to it. The "field" of a current flowing up a straight wire is,
in fact, not unlike the sketch shown in Fig. 4, where instead of tufted
groups we have a sort of magnetic whirl to represent the lines of force.
The lines of force of the galvanic field are, indeed, circles or curves
which inclose the conducting wire, and their number is proportional
to the strength of the current. In the figure, where the current is
supposed to be flowing up the wire (shown by the dark arrows), the
little arrows show the direction in which a free north pole would be
urged round the wire;[1] a south pole would, of course, be urged round
the wire in the contrary direction. Now, though when we look at the
telegraph wires, or at any wire carrying a current of electricity, we
cannot _see_ these whirls of magnetic force in the surrounding space,
there is no doubt that they exist there, and that a great part of the
energy spent in starting an electric current is spent in producing these
magnetic whirls in the surrounding space. There is, however, one way of
showing the existence of these lines of force; similar, indeed, to
that adopted for showing the lines of force in the field surrounding a
magnet. Pass the conducting wire up through a hole in a card or a plate
of glass, as shown in Fig. 5, and sprinkle filings over the surface.
They will, when the glass is gently tapped, arrange themselves in
concentric circles, the smallest and innermost being the best defined
because the magnetic force is strongest there. Fig 6 is an actual
reproduction of the circular lines produced in this fashion by iron
filings in the field of force surrounding an electric current.
[Footnote 1: It will not be out of place here to recall Ampere's
ingenious rule for remembering the direction in which a current urges
the pole of a magnetic needle. "Suppose a man swimming in the wire with
the current, and that he turns so as to face the needle, then the north
pole of the needle will be deflected toward his left hand."]
[Illustration: Fig. 4]
This experimental evidence must suffice to establish two of the three
fundamental points stated at the outset, for they prove conclusively
that the electric current may be treated as a magnetic phenomenon, and
that both in the case of the pole of a magnet, and in that of the wire
which carries a current, a portion, at any rate, of the energy of the
magnetic forces exists outside the magnet or the current, and must be
sought in the surrounding space.
[Illustration: Fig. 5]
[Illustration: Fig. 6]
Having grasped these two points, the next step in our argument is to
establish the relation between the current and the magnet, and to show
how one may produce the other.
[Illustration: Fig. 7]
If we wind a piece of copper wire into a helix or spiral, as in Fig. 7,
and pass a current of electricity through it, the magnetic whirls in the
surrounding space are modified, and the lines of force are no longer
small circles wrapping round the conducting wire. For now the lines of
force of adjacent strands of the coil merge into one another, and run
continuously through the helix from one end to the other. Compare this
figure with Fig. 1, and the similarity in the arrangement of the lines
of force is obvious. The front end of the helix acts, in fact, like the
north pole of a magnet, and the further end like the south pole. If a
small bar of iron be now pushed into the interior of this helix, the
lines of force will run through it and magnetize it, converting it into
an _electro-magnet_. The magnetic "field" of such an electro-magnet is
shown in Fig. 8, which is reproduced from the actual figure made by iron
filings. To magnetize the iron bar of the electro-magnet as strongly as
possible the wire should be coiled many times round, and the current
should be as strong as possible. This mode of making an iron rod or bar
into a powerful magnet is adopted in every dynamo-electric machine. For,
as will be presently explained, very powerful magnets are required, and
these magnets are most effectively made by sending the electric currents
through spiral coils of wire wound (as in Fig. 8) round the bars that
are to be made into magnets.
[Illustration: Fig. 8]
The reader will at this point probably be ready to jump to the
conclusion that magnets and currents are alike surrounded by a sort of
magnetic atmosphere, and such a view may help those to whom the subject
is fresh to realize how such actions as we have been describing can be
communicated from one magnet to another, or from a current to a magnet.
Nevertheless such a conclusion would be both premature and inaccurate.
Even in the most perfect vacuum these actions still go on, and the lines
of force can still be traced. It is probably more correct to conclude
that these magnetic actions are propagated through space not by special
magnetic atmospheres, but by there being movements and pressures and
tensions in the _ether_ which is believed to pervade all space as a
very thin medium more attenuated than the lightest gas, and which when
subjected to electro-magnetic forces assumes a peculiar state, and
gives rise to the actions which have been detailed in the preceding
paragraphs.
[Illustration: Fig. 9.]
The next point to be studied is the magnetic property of a single loop
of the wire through which an electric current flows. Fig. 9 represents
a single voltaic cell containing the usual plates of zinc and copper
dipping into acid to generate a current in the old-fashioned way. This
current flows from the zinc plate through the liquid to the copper
plate, and from thence it flows round the wire ring or circuit back to
the zinc plate. Here the lines of magnetic force in the surrounding
space are no longer only whirls like those drawn in Fig. 4 and 6, for
they react on one another and become nearly parallel where they pass
through the middle of the ring. The thick arrows show the direction of
the electric current, the fine arrows are the lines of magnetic force,
and show the paths along which a free north pole would be urged. All the
front face, where the arrow-heads are, will be like the north pole of a
magnet. All the other face of the ring will be like the south pole of a
magnet. Our ring resembles a flat magnet, one face all north pole the
other face all south pole. Such a magnet is sometimes called a "magnetic
shell."[1]
[Footnote 1: The rule for telling which face of the magnetic shell (or
of the loop circuit) is north and which south in its magnetic properties
is the following: If as you look at the circuit the current is flowing
in the same apparent direction as the hands of a clock move, then the
face you are looking at is a south pole. If the current flows the
opposite way round to the hands of a clock, then it is the north pole
face that you are looking at.]
Since the circuit through which the current is flowing has these
magnetic properties, it can attract other magnets or repel them
according to circumstances.
[Illustration: Fig. 10.]
If a magnet be placed near the circuit, so that its north pole, N, is
opposite that side of the circuit which acts as a south pole, the magnet
and the circuit will attract one another. The lines of force that
radiate from the end of the magnet, curve round and coalesce with
some of those of the circuit. It was shown by the late Professor
Clerk-Maxwell, that every portion of a circuit is acted upon by a force
urging it in such a direction as to make it inclose within its embrace
the greatest possible number of lines of force. This proposition, which
has been termed "Maxwell's Rule," is very important, because it can be
so readily applied to so many cases, and will enable one so easily
to think out the actual reaction in any particular case. The rule is
illustrated by the sketch shown in Fig. 10, where a bar magnet has been
placed with its north pole opposite the south face of the circuit of
the cell. The lines of force of the magnet are drawn into the ring and
coalesce with those due to the current. According to Faraday's mode of
regarding the actions in the magnetic field there is a tendency for the
lines of force to shorten themselves. This would occur if either the
magnet were pulled into the circuit, or the circuit were moved up toward
the magnet. Each attracts the other, and whichever of them is free to
move will move in obedience to the attraction. And the motion will in
either case be such as to increase the total number of lines of force
that pass through the circuit. Lest it should be thought that Fig. 10 is
fanciful or overdrawn, we reproduce an actual magnetic "field" made in
the manner described in the preceding article. Fig. 11 is a kind of
sectional view of Fig. 10, the circuit being represented merely by two
circular spots or holes above and below the middle line, the current
flowing toward the spectator through the lower spot, and passing in
front of the figure to the upper hole, where it flows down. Into this
circuit the pole, N, is attracted, the tendency being to draw as many
lines of force as possible into the embrace of the circuit.
[Illustration: Fig. 11.]
So far as the reasoning about these mutual actions of magnets and
currents is concerned, it would therefore appear that the lines of force
are the really important feature to be understood and studied. All our
reasons about the attractions of magnets could be equally well thought
out if there were no corporeal magnets there at all, only collections
of lines of force. Bars of iron and steel may be regarded as convenient
conductors of the lines of force; and the poles of magnets are simply
the places where the lines of force run out of the metal into the air or
_vice versa_. Electric currents also may be reasoned about, and their
magnetic actions foretold quite irrespective of the copper wire that
acts as a conductor; for here there are not even any poles; the lines
of force or magnetic whirls are wholly outside the metal. There is an
important difference, however, to be observed between the case of the
lines of force of the current, and that of the lines of force of the
magnet. The lines of force of the magnet are the magnet so far as
magnetic forces are concerned; for a piece of soft iron laid along the
lines of force thereby becomes a magnet and remains a magnet as long
as the lines of force pass through it. But the lines of force crossing
through a circuit are not the same thing as the current of electricity
that flows round the circuit. You may take a I loop of wire and put the
poles of magnets on each side of it so that the lines of force pass
through in great numbers from one face to the other, but if you have
them there even for months and years the mere presence of these lines
of force will not create an electric current even of the feeblest kind.
There must be _motion_ to induce a current of electricity to flow in a
wire circuit.
Faraday's great discovery was, in fact, that when the pole of a magnet
is moved into, or moved out of, a coil of wire, the motion produces,
while it lasts, currents of electricity in the coil. Such currents are
known as "induced currents;" and the action is called magneto-electric
"induction." The momentary current produced by plunging the magnet pole
into the wire coil or circuit is found to be in the opposite direction
to that in which a current must be sent if it were desired to attract
the magnet pole into the coil. If the reader will look back to Fig. 10
he will see that a north magnet pole is being attracted in from behind
into a circuit round which, as he views it, the current flows in an
opposite sense to that in which the hands of a clock move round. Now,
compare this figure with Fig. 12, which represents the generation of a
momentary induced current by the act of moving the north pole, N, toward
a wire ring, which is in this case connected with a little detecter
galvanometer, G. The momentary current flows round the circuit (as seen
by the spectator from the front) in the _same_ sense as the movement of
the hands of a clock. The induced current which results from the motion
is found, then, to be in a direction exactly opposed to that of the
current that would itself produce the same movement of the magnet pole.
If the north pole, instead of being moved toward or into the circuit,
were moved away from the circuit, this motion will also induce a
transient current to flow round the wire, but this time the current will
be in the same sense as that in Fig. 10, in the opposite sense to that
in Fig. 12. Pulling the magnet pole away sets up a current in the
reverse direction to that set up by pushing the pole nearer. In both
cases the currents only last while the motion lasts.
[Illustration: Fig. 12.]
Now in the first article it was pointed out that the lines of force of
the magnet indicate not only the direction, but the strength of the
magnetic forces. The stronger the pole of the magnet is, the greater
will be the _number of lines of force_ that radiate from its poles. The
strength of the current that flows round a circuit is also proportional
to the number of lines of force which are thereby caused to pass (as in
Fig. 9) through the circuit. The stronger the current, the more numerous
the lines of force that thread themselves through the circuit. When a
magnet is moved near a circuit near it, it is found that any alteration
in the number of lines of force that cross the circuit is accompanied
by the production of a current. Referring once more to Fig. 10, we will
call the direction of the current round the circuit in that figure the
_positive_ direction; and to define this direction we may remark that if
we were to view the circuit from such a point as to look along the lines
of force in their own direction, the direction of the current round
the circuit will appear to be the same as that of the hands of a clock
moving round a dial. If the magnet, N S, be now drawn away from the
circuit so that fewer of its lines of force passed through the circuit,
experiment shows the result that the current flowing in circuit will be
for the moment increased in strength, the _increase_ in strength being
proportional to the rate of _decrease_ in the number of lines of force.
So, on the other hand, if the magnet were pushed up toward the circuit,
the current in the circuit would be momentarily reduced in strength, the
decrease in strength in the current being proportional to the rate of
increase in the number of lines of force.
Similar considerations apply to the case of the simple circuit and the
magnet shown in Fig. 12. In this circuit there is no current flowing so
long as the magnet is at rest; but if the magnet be moved up toward
the circuit so as to _increase_ the number of lines of force that pass
through the circuit, there will be a momentary "inverse" current induced
in the circuit and it will flow in the _negative_ direction. While if
the magnet were moved away the _decrease_ in the number of lines of
force would result in a transient "direct" current, or one flowing in
the _positive_ direction.
It would be possible to deduce these results from an abstract
consideration of the matter from the point of view of the principle of
conservation of energy. But we prefer to reserve this point until a
general notion of the action of dynamo-electric machines has been given.
The following principles or generalized statements follow as a matter of
the very simplest consequence from the foregoing considerations:
(a) To induce a current in a coil of wire by means of a magnet there
must be relative motion between coil and magnet.
(b) Approach of a magnet to a coil or of a coil to a magnet induces
currents in the opposite direction to that induced by recession.
(c) The stronger the magnet the stronger will be the induced currents in
the coils.
(d) The more rapid the motion the stronger will be the momentary
current induced in the coils (but the time it lasts will, of course, be
shorter).
(e) The greater the number of turns in the coil the stronger will be the
total current induced in it by the movement of the magnet.
These points are of vital importance in the action of dynamo electric
generators. It remains, however, yet to be shown how these transient and
momentary induction currents can be so directed and manipulated as to be
made to combine into a steady and continuous supply. To bring a magnet
pole up toward a coil of wire is a process which can only last a very
limited time; and its recession from the coil also cannot furnish a
continuous current since it is a process of limited duration. In the
earliest machines in which the principle of magneto-electric induction
was applied, the currents produced were of this momentary kind,
alternating in direction. Coils of wire fixed to a rotating axis were
moved past the pole of a magnet. While the coil was approaching the
lines of force were increasing, and a momentary inverse current was set
up, which was immediately succeeded by a momentary direct current as the
coil receded from the pole. Such machines on a small scale are still to
be found in opticians' shops for the purpose of giving people shocks. On
a large scale alternate current machines are still employed for certain
purposes in electric lighting, as, for example, for use with the
Jablochkoff candle. Large alternate-current machines have been devised
by Wilde, Gramme, Siemens, De Meritens, and others.--_Engineering_.
* * * * *
ON THE UNIT WEIGHT AND MODE OF CONSTITUTION OF COMPOUNDS.
Dr. Odling delivered a lecture on the above before the Chemical Society,
London, February 2, 1882.
The lecturer said that it had been found useful to occasionally bring
forward various points of chemical doctrine, on which there were
differences of opinion, to be discussed by the society. On this occasion
he wished not so much to demonstrate certain conclusions, or to make a
declaration of his opinions, as to invite discussion and a thoughtful
consideration of questions of importance to chemists. Originally three
questions were proposed: First, Is there any satisfactory evidence
deducible of the existence of two distinct forms of chemical combination
(atomic and molecular)? Second, Is the determination of the vapor
density of a body alone sufficient to determine the weight of the
chemical molecule? Third, In the case of an element forming two or more
distinct series of compounds, e.g., ferrous and ferric salts, is the
transition from one series to another necessarily connected with the
addition or subtraction of an even number of hydrogenoid atoms? He
would, however, limit himself to the first of these questions; at the
same time the three questions were so closely associated with one
another that in discussing the first it was difficult to know where to
begin. The answer to this question (Is there any satisfactory
evidence deducible of the existence of two distinct forms of chemical
combination?) depends materially on the view we take of the property
called in text-books valency or atomicity; and before discussing the
question it is important to have a clear idea of what these words
valency and atomicity really mean. It is necessary, too, to start with
some propositions which must be taken for granted. These propositions
are: First, that in all chemical changes, those kinds of matter which we
commonly call elementary, do not suffer decomposition. Second, That the
atomic weights of the elements as received are correct, i.e., that they
do really express with great exactitude the relative weights of the
atoms of the individual elements. If we accept these two propositions,
it follows that hydrogen can be replaced atom for atom by other elements
not only by the hydrogens but by alkali metals, etc. Hydrogen is, it may
here be remarked, an element of unique character; not only can it be
replaced by the elements of the widely different classes represented by
chlorine and sodium, but it is the terminal of the series of paraffins,
C_{n}H_{2n}; C_{3}H_{6}, C_{2}H_{4}, H_{2}. The third proposition which
must be taken for granted is, that the groups of elements, C_{2}H_{5},
CH_{3}, behave as elements, and that these radicals, ethyl, methyl,
etc., do not suffer decomposition in many chemical reactions.
Now as to valency or atomicity, accepting the received atomic weights of
the elements, it is certain that there are at least four distinct types
of hydrogen compounds represented by ClH, OH_{2}, NH_{3}, CH_{4}. The
recognition of these types, and their relations to each other as
types, was one of the most important and best assured advances made in
theoretical chemistry. When we compare the formula of water with that of
hydrochloric acid, we find that there is twice as much hydrogen combined
with one atom of oxygen as there is combined with one atom of chlorine;
and in a great many other instances, we find that we can replace two
atoms of chlorine by one atom of oxygen, so that we get an idea of the
exchangeable value of these elements, and we say that one atom of oxygen
is worth two of chlorine, or is bivalent; similarly, nitrogen is said to
be trivalent. The meaning attached to the word "valency," is simply one
of interchangeability, just as we say a penny is worth two halfpennies
or four farthings. The question next arises, is the valency of an
element fixed or variable? If the word be defined as above, it is
absolutely certain that the valency varies. Thus, tin may be trivalent,
SnCl_{2}, or tetravalent, SnCl_{4}. Accordingly elements have been
classed as monads, dyads, triads, etc. The lecturer objected most
strongly to the word "atomicity;" he could not conceive of one atom
being more atomic than another; he could understand the atomicity of
a molecule or the equivalency of an atom, but not the atomicity of an
atom; the expression seemed to him complete nonsense. He next considered
the possibility of assigning a fixed limit to this valency or adicity of
an atom, and concluded that the adicity was not absolutely fixed, but
was fixed in relation to certain elements, e.g., C never combines with
more than four atoms of H; O never more than two atoms of H, etc. The
adicity of an element when combined with two or more elements is usually
higher than when combined with only one, e.g., NH_{3}, NH_{4}Cl. The
term "capacity of saturation," may be used as a synonym for adicity, if
care be taken to distinguish it from other kinds of saturation, such as
an acid with an alkali, etc. Adicity is, however, quite distinct from
combining force; the latter is indicated by the amount of heat evolved
in the combination.
The lecturer then proceeded to criticise a statement commonly found
in text books, that chemical combination suppresses altogether the
properties of the combining bodies. The reverse of this statement is
probably true. To take the case commonly given of the combination of
copper and sulphur when heated; this is good as far as it goes, but
there are numerous instances, as ClI, SSe, etc., where the original
properties and characters of the combining elements do not completely
disappear. The real statement is that the original properties of the
elements disappear more or less, and least when the combination is weak
and attended with the evolution of a slight amount of heat, and in every
case some properties are left which can be recognized. So with reference
to the question of atomic and molecular combination, as atomic
combination does not necessarily produce change, it does not differ in
this respect from what is usually called molecular combination.
The lecturer then referred to an important difference in the adicity of
chlorine and oxygen. Chlorine can combine with methyl or ethyl singly.
Oxygen can combine with both and hold them together in one molecule. The
recognition of this fundamental difference between chlorine and oxygen,
this formation of double oxides as opposed to single chlorides, marks an
epoch in scientific chemistry.
The lecturer then considered the subject of chemical formulae; it is the
bounden duty of every formula to express clearly the number of atoms of
each kind of elementary matter which enters into the constitution of the
molecule of the substance. A formula may do much more than this. If we
attempt to express too much by a complex formula we may veil the number
of atoms contained in it. This difficulty may be avoided by using two
formulae, a synoptic formula giving the number of atoms present, and a
complex formula perhaps covering half a page, giving the constitution
of the molecule. But between the purely synoptic formula and the very
elaborate formula there are others--contracted formulae--which labor
under the disadvantage, as a rule, of being one-sided, and so create a
false impression as to the nature of the substance. Thus, for instance,
to take the formula of sulphuric acid, H_{2}SO_{4}. This suggests that
all the oxygen is united to the S; (HO)_{2}SO_{2} suggests that two
atoms of hydroxyl exist in the molecule; then, again, we might write the
formula HSO_{2}OH, or H_{2}OSO_{3}. All of these are justifiable, and
each might be useful to explain certain reactions of sulphuric acid, but
to use one only creates a false impression. The only plan is to use them
variously and capriciously, according to the reaction to be explained.
Again, ethyl acetate may be written--
H_{3}C\
H_{2}C/
\
O
/
OC\
H_{3}C/
Or condensed--
H_{5}C_{2} \
}O
H_{3}C_{2}O/
Or H_{5}C_{2}O.C_{2}H_{3}O, or H_{5}C_{2}.C_{2}H_{3}O_{2}. Now each
of these two latter formulae is a partial formula, each represents a
one-sided view; it is justifiable if you use both, but unfair if you use
only one.
We now come to the question as to the existence or non-existence of
two distinct classes of compounds, one in which the atoms are combined
directly or indirectly with each other, and the other in which a group
of atoms is combined as an integer with some other group of atoms,
without any atomic connection by so-called molecular combination. These
two modes of combination are essentially distinct. The question is not
one of degree. Are there any facts to support this theory that one set
of compounds is formed in one way, another in a different way? Take the
case of the sulphates: Starting with SO_{3}, we can replace one atom
of O by HO_{2}, and obtain SO_{2}(HO)_{2} or H_{2}SO_{4}; replacing a
second atom, we get SO(HO)_{4} or H_{4}SO_{5}, glacial sulphuric acid, a
perfectly definite body corresponding to a definite class of sulphates,
e.g., H_{2}MgSO_{5}, Zn_{2}SO_{5}, etc. By replacing the third atom of O
we get S(HO)_{6} or H_{6}SOH_{6}; this corresponds to a class of salts,
gypsum, H_{4}CaSO_{6}, etc. These are admitted without dispute to be
atomic compounds. Are we to stop here? We may write the above compounds
thus: H_{2}SO_{4}, H_{2}SO_{4}H_{2}O, H_{2}SO_{4}2H_{2}O. If we measure
the heat evolved in the formation of the two latter compounds, it is,
for H_{2}SO_{4}+H_{2}O, 6.272; H_{2}SO_{4}+2H_{2}O, 3.092. But if we now
take the compound H_{2}SO_{4}+3H_{2}O we have heat evolved 1.744; so we
can have H_{2}SO_{4}4H_{2}O, etc. Where are we to draw the line between
atomic and molecular combination, and why? It comes to this: All
compounds which you can explain on your views of atomicity are atomic,
and all that you cannot thus explain are molecular. Similarly with
phosphates, arsenates, etc. In all these compounds it is impossible to
lay one's finger on any distinction as regards chemical behavior between
the compounds called atomic and those usually called molecular.
Two points remain to be mentioned: The first is the relationship between
alteration of adicity and two series (ous and ic) of compounds. Tin is
usually said to be dyad in stannous compounds and a tetrad in stannic
compounds, but in a compound like SnCl_{2}AmCl, is not tin really a
tetrad?
{Cl
{Cl
Sn {Cl
{NH_{4}
and yet it is a stannous compound, and gives a black precipitate with
H_{2}S; so that valency does not necessarily go with the series. The
second point is that an objection may be urged, as, for example, in
ammonium chloride (the lecturer stated above that here N was a pentad,
the addition of the chlorine having caused the N to assume the pentadic
character), it may be said, why should you not suppose that it is the
chlorine "which has altered its valency, and that the compound should be
written:
{H
{H
N { \
{H--Cl
{H/
There is something to be said for this view, but on the whole the
balance of the evidence is in favor of nitrogen being a pentad.
In conclusion the lecturer stated that his principal object was to
direct the attention of chemists, and especially of young chemists, to
the question: Is there or is there not any evidence derived from
the properties, the decompositions, or the relative stabilities of
substances to warrant us in believing that two classes of compounds
exist: one class in which there is interatomic connection alone, and
another in which the connection is molecular?
* * * * *
FRENCH TOILET ARTICLES.
Mr. Martenson, of St. Petersburg, who, it will be remembered, was one of
the Russian delegates to the International Pharmaceutical Congress, has
been analyzing a number of French preparations for the toilet, most of
which are familiar to our readers, at any rate by name and repute.
1. _Eau de Fleurs de Lys_--(Planchon and Riet, Paris.)--An infallible
banisher of freckles, etc., etc. The bottle contains 100 grammes of
a milky fluid, made up of 97 per cent. of water, 2.5 per cent. of
precipitated calomel, and a small quantity of common salt and corrosive
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